1. Field of the Invention
The invention relates to the field of combustion technology. It relates to a grate for a firing plant, having at least one grate track with a plurality of fixed and moving rows of grate-lining units, which rows alternate in the longitudinal direction, are bounded on both sides by side walls and in each case comprise at least one grate-lining unit provided with feed and discharge lines and with cooling passages, the grate-lining units being pivotably connected in each case in the region of their rear end to a fixed or movable grate-lining bearer and being movably arranged with their front end on or above the following grate-lining unit, and the grate-lining units of a row of grate-lining units in each case being connected by connecting means, arranged below the same, in such a way that adjacent grate-lining units are pivotable to a limited extent relative to the grate-lining bearer allocated to them.
In this case, the invention makes reference to a prior art as disclosed, for example, by Swiss Patent 684 118.
2. Discussion of Background
Grates of the generic type mentioned at the beginning serve to burn and at the same time convey combustion material further and are used in particular in refuse incineration plants.
In addition to air-cooled grate-lining units, also called grate bars or grate plates, water-cooled grate-lining units have been used for years. This is because changes in the composition of waste have led to considerable increases in the calorific value and thus to higher grate wear and higher operating costs. The use of primary air as cooling medium is therefore no longer adequate for these purposes.
German Patent Application St 942 V/24f discloses a stoking grate which consists of alternately fixed and movable rows of grate bars, the fixed rows of grate bars consisting of cooling tubes which lie transversely to the grate direction and are connected in the boiler cooling-water circuit and to which grate bars partly enclosing the tubes are fastened in a close-fitting manner, the cooling tubes being arranged at a constant distance from one another.
Only a very modest cooling effect can be achieved with this solution. On the one hand, only the fixed rows of grate bars can be cooled, since the cooling tubes span the entire grate widthwise. On the other hand, the cooling effect decreases in the transverse direction of the row of grate bars, so that the side of the row of grate bars at which the cooling water is discharged is subjected to greater thermal loading than the side at which the cooling water is fed.
Furthermore, German Patent 498 538 discloses a water-cooled stepped grate having movable grate members. Grate steps are described which are downwardly staggered like stairs and in which cooling water flows transversely to the longitudinal direction of the grate, i.e. transversely to the transport direction of the combustion material, in water troughs which are arranged transversely to the individual steps, are closed by a loosely mounted lid and directly cool only the center region of the grate step. The feed and discharge tubes for the cooling liquid are located in each case at the opposite ends of the trough. A disadvantage with this prior art is that the cast-on comb-like grate bars, which are especially subjected to thermal loading, are not directly cooled in this technical solution.
The thrust combustion grate disclosed by Swiss Patent 684 118 has a grate plate which consists of an essentially rectangular sheet-metal hollow body which has a connecting piece on one side of its underside and a discharge piece on the other side of its underside for the feed and discharge of a cooling fluid flowing through the hollow body. The feeding of primary air is effected via a multiplicity of tubular elements running through the hollow space, the primary-air feed being individually metered for each tubular element.
A disadvantage with this prior art is that, apart from the expensive manufacture of the grate plate, no differentiation of the cooling of the cooling element is possible, although it is known that the thermal loading on the grate lining changes to a great extent in the longitudinal direction of the grate. The undifferentiated cooling has the disadvantage that different temperatures are produced in the element, which contribute to internal stresses and possible corrosion. Furthermore, the cooling space in this solution is substantially larger than the feed and discharge lines. Where there are changes in cross section, however, there is the risk of particles being deposited, e.g. corrosion products and dirt, and thus of the flow pattern and the heat transfer changing in the course of time. In addition, an abrupt change in cross section promotes the formation of vortices, so that air bubbles can be left in the cooling passage, a factor which influences the heat transfer and may also lead to erosion.
Furthermore, EP 0 663 565 A2 discloses a grate bar having a cooling arrangement and a feed and discharge opening arranged in the grate bar, in which at least one passage for directing cooling water runs essentially in the longitudinal direction of the grate bar. The passage arranged in the grate bar preferably has two essentially parallel sections with a direction of flow opposed to one another, these sections being connected to a return point arranged in the head region of the grate bar. A disadvantage with this prior art is that, here, too, no differentiation of the cooling in the longitudinal direction and thus no adaptation to the progression of the thermal loading can be effected.
As a rule, funnel-shaped underblast zones are nowadays made underneath the grate rows. This funnel shape often limits the accessibility to the marginal zones of the grate, in particular for the feed and discharge hoses, which require a movement in one plane so as not to be exposed to any torsional stress.